Nuchal translucency measurements in consecutive normal pregnancies. Is there a predisposition to increased levels?

Objective: The current study aims to assess the relative risk of isolated increased nuchal translucency (NT) in consecutive normal pregnancies. Methods: A retrospective search of the fetal medicine unit database in which NT assessment was conducted. Only singleton fetuses with an unremarkable pregnancy outcome were included in this study. The repeated NT either at a threshold of >2.5 mm or ≥95th centile of the normal range for various CRLs (2 mm at a CRL ≤44 mm to 2.85 mm at CRLs 83-84 mm) was assessed. Pearson's correlation was applied to investigate any correlation between a log₁₀ NT obtained in two consecutive pregnancies. The chance of an increased NT in the first pregnancy followed by similar results in the subsequent one was assessed using Fisher's exact test. Results: Ninety-two pregnant women with two consecutive normal pregnancies were identified. There was a highly significant correlation between the log₁₀ NT values measured in the consecutive pregnancies (r = 0.38; p < 0.001). The relative risk of an isolated NT ≥2.5 mm in the first pregnancy to be followed by a similar finding in the subsequent one was 18.21 (95% confidence interval [CI]: 3.62-91.55). The relative risk of an isolated NT ≥95th centile in the first pregnancy to be followed by a similar result in the subsequent one was 21 (95% CI: 4.53-97.44). Conclusion: The current results indicate a significant correlation of NT values in consecutive unaffected pregnancies. There also was a predisposition for a repeated isolated increased NT in subsequent pregnancies. Additional series and more information are needed before firm conclusions can be made.